Frost-resistant steam circuit process device and its method of operation

ABSTRACT

The invention concerns a steam circuit process device comprising a reservoir for a liquid working medium; a feed pump for supplying working medium from the reservoir to an evaporator, in which the working medium is evaporated; an expander, to which vaporised working medium is fed by the evaporator, which expands by way of performing mechanical work in the expander; a condenser, which follows the expander and is in fluid connection with the reservoir, whereas the working medium is liquefied in the condenser; The invention is characterised in that the steam circuit process device includes an emptying pump for the working medium which is arranged in a by-pass line between the reservoir and a switchable valve system in fluid communication with at least one further component of the steam circuit process device.

The invention concerns a frost-resistant steam circuit process device and its method of operation, whereas the steam circuit process device is arranged stationary or presents a mobile application and can be mounted in particular in a vehicle, to assist the vehicle propulsion or to be used to drive auxiliary units.

Steam circuit processes, such as Clausius-Rankine- or ORC-processes (Organic Rankine Cycle) are used for converting thermal energy into mechanical energy. Heat can for instance be input via a separate burner unit of a heat and electricity cogeneration device. Heat sources which can be fed for efficient energy consumption of a steam circuit process device, for applications in vehicles fitted with internal combustion engines as drive motors, are available with the exhaust gas and cooling water flow of the internal combustion engine. See for instance document WO 2008/138562 A1.

Devices for carrying out a Clausius-Rankine process typically comprise a reservoir for a vaporisable working medium, out of which a feed pump scoops liquid working medium and conveys it to an evaporator under pressure. The evaporator is in fluid connection to an expander and conveys vaporised working medium thereto, which expands with a simultaneous release of power in the expander. A condenser follows the expander for renewed liquefaction of the working medium, out of which the working medium is returned in liquid phase to the reservoir. An additional condensate pump for supplying liquid can be used between the expander and the reservoir. Such a device is disclosed for instance in document CH 371813.

Feed pumps for supplying the working medium to the evaporator are set to high operating pressure, for instance 30-200 bar, and are typically unidirectional. Feed pumps with variable volume flow rate are preferred for controlling the steam circuit process device. These can for instance be designed in the form of an internal gear pump. The use of a feed pump cascade may be envisaged. See for instance document U.S. Pat. No. 5,896,746, which describes a high pressure pump configured for 250 bars for a steam circuit process device with a steam storage tank. A circulation pump connected downstream is provided additionally.

A steam circuit process device can be designed for mobile applications and in particular vehicle usages as well as for some stationary plants in such a way that said device also withstands temperatures below freezing point and is startable at sub-zero temperatures. Various antifreeze compounds have been suggested since a water-based working medium is preferred in particular as regards handleability. Document DE 10 2009 003 850 A1 thus describes the addition of a frost protection and/or lubricant component to the liquid phase of the working medium of a Clausius-Rankine process, whereas the water content of the working medium is separated from the frost protection compound, typically glycol, and from the lubricant, by means of a separator, before entering the high temperature ranges of the plant. Such separation processes are however costly and cannot always be carried out completely under normal operating conditions so that smaller amounts of frost protection compounds constantly reach the high temperature ranges and accumulate there or are plagued with uncontrolled thermal decomposition processes.

DE 10 2006 052 906 A1 therefore provides an addition of low-chain alcohols to water as a working medium of a steam circuit process device, wherein alcohol takes over the frost protection function and remains stable at temperatures above 170° C. so that it can pass through the steam circuit process with the actual working medium.

Alternately, DE 10 2007 020 086 B3 suggests using a working medium with a vaporisable component and a further component in the form of a ionic fluid for operating a steam circuit process device. The ionic fluid should be sufficiently thermally stable in such a way that it can enter the evaporator with the vaporisable component. Consequently, the ionic fluid does not take part itself in the vaporisation process due to the substantially vanishing steam pressure and hence does not reach into the expander and instead of that remains in the liquid phase. For an accordingly chosen ionic fluid, said can take over a frost protection function in the reservoir of the working medium. The addition of a ionic fluid however complicates the vehicle operation since a special working medium is used whose availability should be guaranteed. Moreover, resultant problems also crop up in such a case as regards the toxicity and the environmental compatibility of the involved working medium.

It is referred to documents DE 10 2008 037 744 A1, DE 10 2007 043 373 A1 and DE 102 28 868 B4 to find a publication of the state of the art, which disclose ionic operating fluids for a steam circuit process device as well as a frost-proof feed water tank.

The object of the invention is then to design a steam circuit process device in such a way that frost-proof operation is permitted. Consequently, the system should be characterised by structural simplicity and in particular be usable in association with a vehicle drive, whereas a compact, lightweight system with small space requirements is required, which lends itself for use of a widely available and easy-to-handle working medium.

The object is satisfied by the characteristics of the independent claims.

The invention is based upon a generic steam circuit process device with a reservoir for a liquid working medium, with a feed pump for supplying working medium from the reservoir to an evaporator, in which the working medium is evaporated, with an expander, to which vaporised working medium is fed by the evaporator, which expands by way of performing mechanical work in the expander, and with a condenser, which follows the expander and is in fluid connection with the reservoir. According to the invention, an emptying pump which is decoupled by the fluidic circuit and not used for normal operation, is provided for the emptying of the steam circuit process device after shutting down the plant. Said pump is arranged in a by-pass line between the reservoir and a switchable valve system in fluid communication with at least one further component of the steam circuit process device.

Thereby, the working medium is drawn into the reservoir from the frost-sensitive components of the steam circuit process device by means of the emptying pump after shutting down the plant so that a working medium can be used without additional anti-freeze. For that purpose, a small-sized, but heavy-duty pump, which does not operate in the range of operating pressure of the steam circuit process device, is sufficient. Said pump is advantageously designed with a dry-run capacity and a frost-resistance. A control device is besides associated with the emptying pump, which device is connected at least indirectly to a temperature sensor to determine the surrounding temperature and/or the operating temperature of the steam circuit process device. The control device is more advantageously directly connected to the battery of the vehicle or another power supply so that a stand-alone and fail-safe control unit is available for the emptying pump.

The invention is described more in detail below using exemplary embodiments in connection with figure illustrations. They represent the following in detail:

FIG. 1 is a simplified diagram of a steam circuit process device according to the invention with a feed pump and an emptying pump in fluid connection with a reservoir for the working medium.

FIG. 2 shows an further embodiment of the device of FIG. 1 with an additional fluid connection between the emptying pump and an evaporator of the steam circuit process device.

FIG. 1 is a schematically simplified, symbolic diagram of a steam circuit process device according to the invention with a reservoir 1 for a working medium from which a feed pump 2 scoops. This generates an inflow of liquid working medium with high pressure to the evaporator 3. Said evaporator is operated by an exhaust gas stream 12 out of an internal combustion machine 13, through which the working medium is evaporated. The vapour phase of the working medium is then fed to an expander for expansion by way of performing mechanical work. A condenser 5 follows the expander 4 for renewed liquefaction of the working medium, which again communicates at least indirectly with the reservoir 1 for recirculation of the liquid working medium.

According to the invention an emptying pump 6 is provided which is not actuated in normal operating condition of the steam circuit process device. Under those circumstances, the emptying pump 6 is arranged in a by-pass line 7 which extends between a valve system 8, which is arranged upstream for the present configuration of the feed pump 2, and the reservoir 1. In the illustrated embodiment, the valve system 8 is designed as a switchable 3/2-way valve which enables to create a fluid connection between the reservoir 1 and the feed pump 2 in a first position for normal operation. In said first position, the emptying pump 6 is separated from the fluidic circuit of the steam circuit process device.

In a second position of the valve system 8, a fluid connection is provided between the emptying pump 6 and the feed pump 2. Said second position is initiated by an associated control device 9, which simultaneously controls and/or regulates the operation of the emptying pump 6 once the steam circuit process device has been shut down. It then becomes possible to empty the feed pump 2 in particular as well as the subsequent fluid circuit of the steam circuit process device by means of the emptying pump 6, wherein the evacuated working medium is conveyed to the reservoir 1 via the by-pass line 7.

The working medium is drawn out of the frost endangered regions of the steam circuit process device by means of the emptying pump 6. A working medium freezing at low external temperatures, for instance water, can hence be used without requiring additional frost protection means. It is hence assumed that the working medium can freeze up in the reservoir 1 in the case of long plant standstill and at low surrounding temperatures without damaging the reservoir 1.

To guarantee that no residues of liquid working medium remain in the steam circuit process device through progressive condensation after switch off, the emptying pump is most preferably activated several times with intermediate resting periods. For that purpose there is preferably an at least indirect connection between the control device 9 and a temperature sensor 10 to measure the temperature of individual components of the steam circuit process device and/or the surrounding temperature. In this manner, the condensate of the residual steam which forms during the cool down of the steam circuit process device, is returned to the reservoir 1. This evacuation of the residual medium, which is time-delayed or performed several times, can be carried out in a time and/or temperature-controlled manner.

A control device 9 associated with the emptying pump 6 and which is also used for switching the valve system 8, is besides designed as a stand-alone unit to guarantee reliable shutdown of the steam circuit process device also in the case of a system fault in a superordinate control device. To do so, a separate supply of electricity through direct connection of the control device 9 fitted with a battery 11 of the vehicle is preferred.

The emptying pump 6 does not take part in the normal operation of the steam circuit process device so that there is no necessity to set them to the typically high system pressures. Accordingly, a compact, but heavy-duty pump design can be selected for the emptying pump 6. A construction as a dry-run pump is particularly preferable which is additionally frost-resistant. There is hence the possibility to adapt the feed pump 2 for normal operation of the steam circuit process device of the task associated therewith, especially to design it as a unidirectional pump for high operating pressures with variable discharge volumes. There is accordingly no necessity to build the feed pump 2 with a frost resistance or a dry-run capacity. The emptying pump 6 draws the fluid after switch off.

Additionally, the emptying pump 6 is preferably reversible so that it conveys working medium to the feed pump from the reservoir 1 to start the steam circuit process device, until said pump is flooded sufficiently and can take over operation by itself. In an alternative embodiment, the emptying pump 6 is designed in a simplified fashion as a unidirectional pump and the flooding of the feed pump 2 involves an additional valve system, non-illustrated in detail, which ensures the reversal of direction for the flow of working medium. The pump direction can again be controlled depending on the temperature whereas for instance the volume of working medium is used as a controlled variable in the preferably heatable reservoir 1.

FIG. 2 shows another embodiment of the invention with a first valve system 8.1, by means of which a fluid connection can be created from the emptying pump 6 to the feed pump 2, and a second valve system 8.2, which switches a direct connection between the emptying pump 6 and the evaporator 3. This measure gives the possibility of emptying the evaporator 3 after the shutting down the steam circuit process device separately via the emptying pump 6.

In an alternative embodiment, non-illustrated in detail, a further switchable fluid connection is provided between the expander 3 and the reservoir 1 so that the second valve system 8.2 can be adjusted for the cold start in such a way that the emptying pump 6 triggers a circulation of the working medium from the reservoir 1 through the evaporator 3 and back to the reservoir 1, so as to guarantee first of all a certain basic temperature in the reservoir 1 and in subsequent regions. Consequently it is possible to allocate a heating device 14 to the reservoir 1, which device liquefies a portion of the working medium in the event of a frozen working medium in the reservoir 1. Said medium is then conveyed to the evaporator 3 via the feed pump 2 and is there further warmed up during operation of the internal combustion engine so that heated, however still liquid working medium can be conveyed to the reservoir 1. Alternately to a separate heating device 14 in the reservoir 1, the use of an external heat source, not illustrated in detail, to obtain the basic temperature of the reservoir 1 can be envisioned. In particular an integration into the engine cooling circuit can here be considered whereas preferably in normal operating condition a possibility to separate the heat supply to the reservoir 1 is provided. A by-pass connection to the switchable feed line of the exhaust gas stream leading to a channel system in the envelope of the reservoir 1 is also a possible variation. Additional heat sources in the form of pre-heaters and add-heaters or latent heat accumulators can also be envisioned.

Further embodiments in the context of the protected claims can be envisioned. Consequently, further components of the steam circuit process device, such as a sump in the expander 4, in which the working medium input by blow-by accumulates, or the condenser can be connected to the emptying pump for reliable emptying after shutting down the plant. In that case, the emptying pump according to the invention is provided in a switchable by-pass line also for steam circuit process devices which use a condensate pump connected downstream of the condenser in normal operation.

LIST OF REFERENCE NUMERALS

-   1 Reservoir -   2 Feed pump -   3 Evaporator -   4 Expander -   5 Condenser -   6 Emptying pump -   7 By-pass line -   8 Valve arrangement -   8.1 First valve arrangement -   8.2 Second valve arrangement -   9 Control device -   10 Temperature sensor -   11 Battery -   12 Exhaust gas stream -   13 internal combustion machine -   14 Heating device 

1. A steam circuit process device comprising 1.1 a reservoir (1) for a liquid working medium; 1.2 a feed pump (2) for supplying working medium from the reservoir (1) to an evaporator (3), in which the working medium is evaporated; 1.3 an expander (4), to which vaporised working medium is fed by the evaporator (3), which expands by way of performing mechanical work in the expander (4); 1.4 a condenser (5), which follows the expander (4) and is in fluid connection with the reservoir (1), whereas the working medium is liquefied in the condenser (5); characterised in that 1.5 the steam circuit process device includes an emptying pump (6) for the working medium, which is arranged in a by-pass line (7) between the reservoir (1) and a switchable valve system (8) in fluid communication with at least one further component of the steam circuit process device.
 2. The steam circuit process device according to claim 1, characterised in that the emptying pump (6) is designed as a reversible pump conveying in two flow directions.
 3. The steam circuit process device according to claim 1, characterised in that the emptying pump (6) has a dry-run capability.
 4. The steam circuit process device according to claim 1, characterised in that the emptying pump (6) is frost-resistant.
 5. The steam circuit process device according to claim 1, characterised in that a control device (9) is associated with the emptying pump (6) and the valve system (8), which is connected at least indirectly to a temperature sensor (10) to determine the surrounding temperature and/or the operating temperature of the steam circuit process device.
 6. The steam circuit process device according to claim 5, characterised in that the control device (9) is directly connected to another power supply to ensure power supply with a battery (11).
 7. The steam circuit process device according to claim 1, characterised in that the emptying pump (6) has no dry-run capability and the valve system (8) is connected at least indirectly to the feed pump (2) so that the emptying pump (6) floods the feed pump (2) with working medium during scooping operation from the reservoir (1).
 8. A method for operating a steam circuit process device comprising 8.1 a reservoir (1) for a liquid working medium; 8.2 a feed pump (2) for supplying working medium from the reservoir (1) to an evaporator (3), in which the working medium is evaporated; 8.3 an expander (4), to which vaporised working medium is fed by the evaporator (3), which expands by way of performing mechanical work in the expander (4); 8.4 a condenser (5), which follows the expander (4) and is in fluid connection with the reservoir (1), whereas the working medium is liquefied in the condenser (5); characterised in that 8.5 the working medium is returned to the reservoir (1) after shutdown of the steam circuit process device, by means of an emptying pump (6) for the working medium which is arranged in a by-pass line (7) between the reservoir (1) and a switchable valve system (8) in fluid communication with at least one further component of the steam circuit process device.
 9. The method for operating a steam circuit process device according to claim 8, characterised in that the feed pump (2) is flooded with working medium by the emptying pump (6) during scooping operation when starting the steam circuit process device.
 10. The steam circuit process device according to claim 2, characterised in that the emptying pump (6) has a dry-run capability.
 11. The steam circuit process device according to claim 2, characterised in that the emptying pump (6) is frost-resistant.
 12. The steam circuit process device according to claim 3, characterised in that the emptying pump (6) is frost-resistant.
 13. The steam circuit process device according to claim 2, characterised in that a control device (9) is associated with the emptying pump (6) and the valve system (8), which is connected at least indirectly to a temperature sensor (10) to determine the surrounding temperature and/or the operating temperature of the steam circuit process device.
 14. The steam circuit process device according to claim 3, characterised in that a control device (9) is associated with the emptying pump (6) and the valve system (8), which is connected at least indirectly to a temperature sensor (10) to determine the surrounding temperature and/or the operating temperature of the steam circuit process device.
 15. The steam circuit process device according to claim 4, characterised in that a control device (9) is associated with the emptying pump (6) and the valve system (8), which is connected at least indirectly to a temperature sensor (10) to determine the surrounding temperature and/or the operating temperature of the steam circuit process device.
 16. The steam circuit process device according to claim 2, characterised in that the emptying pump (6) has no dry-run capability and the valve system (8) is connected at least indirectly to the feed pump (2) so that the emptying pump (6) floods the feed pump (2) with working medium during scooping operation from the reservoir (1).
 17. The steam circuit process device according to claim 3, characterised in that the emptying pump (6) has no dry-run capability and the valve system (8) is connected at least indirectly to the feed pump (2) so that the emptying pump (6) floods the feed pump (2) with working medium during scooping operation from the reservoir (1).
 18. The steam circuit process device according to claim 4, characterised in that the emptying pump (6) has no dry-run capability and the valve system (8) is connected at least indirectly to the feed pump (2) so that the emptying pump (6) floods the feed pump (2) with working medium during scooping operation from the reservoir (1).
 19. The steam circuit process device according to claim 5, characterised in that the emptying pump (6) has no dry-run capability and the valve system (8) is connected at least indirectly to the feed pump (2) so that the emptying pump (6) floods the feed pump (2) with working medium during scooping operation from the reservoir (1).
 20. The steam circuit process device according to claim 6, characterised in that the emptying pump (6) has no dry-run capability and the valve system (8) is connected at least indirectly to the feed pump (2) so that the emptying pump (6) floods the feed pump (2) with working medium during scooping operation from the reservoir (1). 